Cercarial/adult (c/a) antibody ratios from acutely infected patients were higher than from individuals with chronic schistosomiasis. Specific IgM titers to soluble egg antigen (sea) were found in all patients with acute or early schistosomiasis but from only a few patients with chronic schistosomiasis. IgM antibody in the chronic patients correlated with the presence of circulating immune complexes. Specific IgE antibody was found in most of the sera from acute patients and in only a few of the ones with chronic schistosomiasis. SEA and toxoplasma antigen added to serum have been detected by ELISA at levels of 10 and 100 ng/ml respectively.